Public Health Surveillance Diane Woolard, Ph.D., M.P.H. Division of Surveillance & Investigation Virginia Department of Health
Objectives of Lecture • Key concepts of surveillance • Definition • Uses • Methods • Public health surveillance systems • Use and evaluation of surveillance systems • Influenza surveillance
What comes to mind when you hear ‘surveillance’? • Law enforcement agencies • CIA • Routine data collection • Statistics • Trends
Definition of Surveillance • The ongoing systematic collection, analysis, and interpretation of outcome-specific data for use in the planning, implementation, and evaluation of public health practice. • Includes data collection, analysis, and dissemination to those responsible for prevention and control.
What Surveillance Is • Systematic, ongoing… • Collection • Analysis • Interpretation • Dissemination • …of health outcome data • Health action • investigation • control • prevention
Surveillance History in U.S. • 1741 – Rhode Island passed an act requiring tavern keepers to report contagious disease • 1850 – Mortality statistics first published by the federal government for the U.S. • 1874 – Massachusetts instituted weekly reporting of diseases by physicians • 1878 – Public Health Service (PHS)-type organization created to collect morbidity data for use in quarantine for cholera, smallpox, plague, yellow fever.
Surveillance History in U.S. • 1901 – All states required disease reporting. • 1925 – All states began participating in national morbidity reporting • 1935 – First national health survey • 1951 – Council of State and Territorial Epidemiologists (CSTE) authorized to determine diseases to be reported to PHS • 1961 – Morbidity and Mortality Weekly Report (MMWR) published
Legal Authority for Surveillance • Legal authority for mandatory public health surveillance resides with states • Virginia Code • 32.1-35 – BOH shall promulgate a list of diseases required to be reported. • 32.1-36 – Physicians and laboratories shall report. • 32.1-37 – Medical care facilities, schools and summer camps shall report.
Virginia Code, continued • 32.1-38 – Anyone making a report is immune from liability • 32.1-39 – BOH shall provide for surveillance & investigation. • 32.1-40 – Commissioner or designee can examine medical records • 32.1-41 – Anyone examining records must preserve anonymity of the patient and the practitioner
Purpose of Surveillance • To assess public health status, to define public health priorities, to evaluate programs, and to stimulate research. • Tells us where the problems are, who is affected, and where the programmatic and prevention activities should be directed.
Estimates of a health problem Natural history of disease Detection of epidemics Distribution and spread of a health event Hypothesis testing Evaluating control and prevention measures Monitoring change Detecting changes in health practice Facilitate planning How can surveillance data be used?
Uses of Surveillance DataEstimates of a Health Problem • Quantitative estimates of the magnitude of a health problem • including sudden or long-term changes in trends, patterns
Uses of Surveillance DataNatural History of Disease • Portrayal of the natural history of disease (clinical spectrum, epidemiology) Varicella Cases by Month – Antelope Valley, CA, 1995–2004
Uses of Surveillance DataDetection of Epidemics SALMONELLOSIS Incidence,* by year United States, 1973-2003 *Per 100,000 population Slide from CDC 2003 Annual Summary
Uses of Surveillance Data Distribution & Spread of a Health Event • West Nile Virus in the US, 2000-2003 2000 2001 2002 2003
Use of Surveillance DataHypothesis Testing • Facilitation of epidemiologic and laboratory research • Hypothesis testing PERTUSSIS Number of reported cases*, by age group United States, 2003 *Of 11,647 cases, age was reported unknown for 46 (0.4%) cases. Slide from CDC – 2003 Annual Summary
Uses of Surveillance Data Evaluating control & prevention measures Effectiveness of vaccine introduction
Uses of Surveillance DataMonitoring changes • Monitoring changes in infectious agents and host factors National Nosocomial Infections Surveillance System
Uses of Surveillance DataFacilitate Planning • Identify target populations in need of health services • Refugee populations • Morbidity surveillance in emergency shelters • Identify health topics to be addressed by educational programs and media
Outcomes • Surveillance is outcome oriented • Can measure frequency of an illness or injury, severity of the condition, and impact of the condition. • Number of cases, incidence, prevalence; case fatality, hospitalization rate, mortality, disability; cost. • Orient data by person, place, and time.
Planning a Surveillance System • Establish objectives • Develop case definitions • Determine data source or data collection mechanism • Field test methods • Develop and test analytic approach • Develop dissemination mechanism • Assure use of analysis and interpretation
What Should be Under Surveillance? • Establish priorities based on: • Frequency (incid., prev., mortality, YPLL) • Severity (case-fatality, hospitalization rate, disability rate) • Cost (direct and indirect) • Preventability • Communicability • Public interest • Will the data be useful for public health action?
Surveillance MethodsCase Definition • Case definition • Important to clearly define condition • Ensures same criteria are used by all • Makes the data more comparable • Include person, place, time • May define suspected and confirmed cases • May include symptoms, lab values, time period, population as appropriate
Case Definition Examples • Weak Definition - Measles • Any person with a rash and fever, runny nose, or conjunctivitis • Better Definition - Measles • Any person with a fever >101 F, runny nose, conjunctivitis, red blotchy rash for at least 3 days, and laboratory confirmation of IgM antibodies • Clinical, Probable, Confirmed Case Definitions • Outbreak Case Definition • Differs from routine surveillance • Epidemiologically linked
Surveillance MethodsData Collection • Data collection • Standardized instruments, field tested • Passive Surveillance • Providers are responsible for reporting. • Health dept. waits to receive reports. • Problem with underreporting • Active Surveillance • Providers contacted on regular basis to collect information • More resource intensive • Used for outbreaks or pilots (e.g., HUS)
Surveillance MethodsData Analysis • Ongoing review • Descriptive statistics, Multivariate analyses • Automated analyses
Surveillance MethodsInterpretation and Dissemination • Presentation of data in the form of tables, graphs, maps, etc. • Disseminate data via reports, presentations, internet, etc.
Surveillance Methods Evaluation • Did the system generate needed answers to problems? • Was the information timely? • Was it useful for planners, researchers, etc? • How was the information used? • Was it worth the effort? • What can be done to make it better? • (More on evaluation later).
Cycle of Surveillance • Data Collection • Pertinent, regular, frequent, timely • Consolidation and Interpretation • Orderly, descriptive, evaluative, timely • Dissemination • Prompt, to all who need to know (data providers and action takers) • Action to Control and Prevent • Evaluation
Data Sources • Vital Statistics • Notifiable Diseases • Registries • Sentinel Surveillance • Syndromic Surveillance • Surveys • Administrative Data
Data Sources: Vital Statistics • Live Births • Deaths • Fetal Deaths • Marriages • Divorces • Induced Terminations of Pregnancy • Infant Mortality (link birth and death data)
Virginia Death Certificate SAMPLE
Uses of Vital Statistics Data • Monitoring long-term trends • Identifying differences in health status within racial or other population subgroups • Assessing differences by geographic area • Monitoring deaths that are preventable • Generating hypotheses about causation • Monitoring progress toward improved health of the population; health-planning
Vital Records: Coding and Calculating • ICD-9 historically, now ICD-10 • Infant mortality - need number of live births for denominator in calculating rates • Other death rates - use total population in rate calculations. • Crude and adjusted (standardized) rates used.
Quality of Vital Stats Depends on • Care taken by health care providers in ascertaining cause of death and other factors • Accuracy of coding (difficult for injuries) • Relevance of existing codes for the condition being recorded • Accuracy of population estimates • Problems - don’t know onset, can’t see effect of diseases that don’t lead to death
Data Sources: Notifiable Diseases • States decide what is notifiable/reportable • Based on disease occurrence, potential for outbreaks, public perception of risk, etc. • CSTE recommendations • Different processes for generating N.D. list • Weekly (or sometimes rapid) reporting to health departments by physicians, medical care facilities, laboratories. • States report to CDC
Reportable Disease List Over 70 reportable diseases/conditions
Chain of Communication Other States State Providers Patients Public Central Office Regional Epis Local H.D. CDC Other Health Districts Add this in 2009
Human Arbovirus Infections Since 1975 WNV (67 cases)* SLE (8 cases)* LAC (29 cases)* EEE (5 cases)* *Number of cases through 9/08 Geographic Distribution of Human Arbovirus Cases Recorded in Virginia since 1975 WNV = West Nile virus LAC = La Crosse encephalitis virus SLE = St. Louis encephalitis virus EEE = Eastern equine encephalitis virus
Limitations of Disease Reporting • Underreporting • Reporting better for more serious diseases and those for which there is laboratory confirmation • Need to seek medical consultation to be diagnosed and then reported • Lack of representativeness of reported cases • Inconsistent case definitions
Reasons for Not Reporting • Assume someone else reported. • Did not know reporting was required; don’t have a copy of the reportable disease list. • Do not know how to report; don’t have form or telephone number. • Concern about confidentiality and doctor-patient relationship. • No incentive to report. Time-consuming. Unaware of value.
How to Improve Reporting • Contact physicians in the community • Tell them the health department is very interested in morbidity reporting • Maintain a reasonable list of reportable diseases • Maximize contact through presentations, mailings, newsletters, media, etc. • Use the data